The cutting of moving strip material has been carried out in a variety of ways. In one relatively primitive method, the moving strip was temporarily stopped at a point just before a shear blade, and the shear blade was operated. Upstream of the shear blade the strip continued to move and formed a loop. Once the shear blade opened, the strip was then allowed to pass forwardly again and the loop was removed. Other systems have involved pairs of upper and lower shears which were mounted on rails and could move forwardly and backwardly along the axis of the sheet material. By accelerating the upper and lower shear dies to the speed of the sheet material, the dies could then be closed, without stopping the sheet material. The dies would then be opened up and stopped and returned to their starting position for the next cut. These systems were effective but the mechanism was complex and expensive. It was also difficult to achieve a precise location for the position of each cut. In addition, cuts of less than a predetermined length could not be achieved at all due to the fact that the shear dies had to move forwardly and backwardly once during each cut.
U.S. Pat. No. 2,445,174 involved rotary blades which essentially chopped the web material at predetermined locations. However, controlling the length of cut on these rotary choppers was difficult, since the length of cut depended on upon the diameter of the chopper drum, and the speed of the web requiring changes in gears.
Clearly there is a need for a rotary cutoff device which is capable of cutting moving web sheet material at predetermined locations, the locations being adjusted and pre-settable, and being operable even at over relatively short distances between cuts, and involving a minimum of complex machinery.